Krusty's got it right. Here's the Wiki definition of a turboprop, almost word for word how Krusty described:
A Turboprop engine is a type of gas turbine engine used in aircraft. Most of a turboprop engine's power is used to drive a propeller, and the propellers used are very similar to the propellers used in piston or reciprocating engine-driven aircraft (with the exception that turboprops usually use a constant velocity propeller).
A turboprop engine is similar to a turbojet, but has additional fan blades in the turbine stage to recover more power from the engine to turn the propeller. Turboprop engines are generally used on small or slow subsonic aircraft, but some aircraft outfitted with turboprops have cruising speeds in excess of 500 kts (926 km/h, 575 mph).
In its simplest form, a turboprop consists of an intake, compressor, combustor, turbine and a propelling nozzle. Air is drawn into the intake and compressed by the compressor. Fuel is then added to the compressed air in the combustor. The hot combustion gases expand through the turbine. Part of the power generated by the turbine is used to drive the compressor. The rest, goes through the reduction gearing, to the propeller. Further expansion of the gases occurs in the propelling nozzle, where the gases exhaust to atmospheric pressure. The propelling nozzle provides a relatively small proportion of the thrust generated by a turboprop, the remainder comes from the conversion of shaft power to thrust in the propeller.
Turboprops are very efficient at modest flight speeds (below 450 mph), because the jet velocity of the propeller (and exhaust) is relatively low. Due to the high price of turboprop engines, they are mostly used where high performance Short-Takeoff and Landing (STOL) capability and efficiency at modest flight speeds is required. In a civilian aviation context, the most common application of turboprop engines are small commuter aircraft.
